Soybean Insect Pests

— Written By Hunter Rhodes and last updated by
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Farmers of all crops here in Sampson County often deal with a plethora of insect pests throughout the growing season. These insects can wreak havoc in fields in a matter of days depending on the growth stages of certain crops. From now until mid-September, it is crucial for growers to scout their soybean fields for certain insects to ensure they make timely and effective pesticide applications. However, fields flowering from now until the end of August should be given priority for scouting because they are the most susceptible to insect damage that can lead to yield loss. While there are many crucial insects that can be found in a soybean field, we will focus mainly on corn earworms and stinkbugs because they feed on flowers and pods, which cause direct yield loss.

The corn earworm often functions as a foliage-feeder and is described under foliage-feeding caterpillars during most growth stages of the soybean plant. However, it prefers to eat blooms and pods. Therefore, when plants are in the reproductive growth stage this caterpillar is sampled as a pod feeder. The corn earworm causes more damage than any other insect on soybeans in North Carolina. Its feeding can reduce yields and delay plant maturity. Corn earworm moths are attracted to soybean fields that are blooming, typically laying more eggs in open canopied beans that are generally found on light soils or high areas of the field.

Stink bugs are shield shaped insects that affect fruiting soybeans and reach peak populations in late August through early October, primarily in mid-September. However, their populations can remain active in fields until the first frost. While they do not always reach population levels in soybeans high enough to cause significant yield loss, stink bugs are important to scout during late season because high populations can damage both yield and quality. Scouting for stink bugs can be done simultaneously while scouting for corn earworms since the methods for scouting are the same.

There are many foliar feeding insects that can cause damage to soybeans. While we won’t go into specific insects, foliar damage in soybeans due to foliage feeders is usually simple to evaluate. The threshold for foliar feeding pests is 30% loss throughout the canopy during the vegetative stages up to two weeks prior to flowering and 15% foliage loss throughout the canopy two weeks prior to flowering through the reproductive stages up to R6-R7.

These insects are very different in how they feed on the soybean plant and the damage they can cause. They also require different pesticide applications and do not fall under an umbrella “one size fits all” treatment. Treatment of one specific insect can also cause a spike in other insect populations. Therefore, it is vital for growers to scout individual fields, or at least individual soybean varieties and planting dates, to ensure they are making informed decisions when making applications.

For more information on scouting methods, soybean insects, and more please contact Hunter Rhodes at the North Carolina Cooperative Extension office in Sampson County at 910-592-7161.